The author examines the ability of left atrial size and function to predict cardiovascular outcomes. Data are sufficient to recommend evaluation of left atrial volume in certain populations, and although analysis of atrial reservoir, conduit, and booster pump function trails in that regard, the gap is rapidly closing. In this state-of-the-art paper, the author reviews the methods used to assess left atrial size and function and discusses their role in predicting cardiovascular events in general and referral populations and in patients with atrial fibrillation, cardiomyopathy, ischemic heart disease, and valvular heart disease.

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Increases in type 1 phosphatase (PP1) activity have been observed in end stage human heart failure, but the role of this enzyme in cardiac function is unknown. To elucidate the functional significance of increased PP1 activity, we generated models with (i) overexpression of the catalytic subunit of PP1 in murine hearts and (ii) ablation of the PP1-specific inhibitor. Overexpression of PP1 (threefold) was associated with depressed cardiac function, dilated cardiomyopathy, and premature mortality, consistent with heart failure. Ablation of the inhibitor was associated with moderate increases in PP1 activity (23%) and impaired ␤-adrenergic contractile responses. Extension of these findings to human heart failure indicated that the increased PP1 activity may be partially due to dephosphorylation or inactivation of its inhibitor. Indeed, expression of a constitutively active inhibitor was associated with rescue of ␤-adrenergic responsiveness in failing human myocytes. Thus, PP1 is an important regulator of cardiac function, and inhibition of its activity may represent a novel therapeutic target in heart failure.